Shift control system for automatic transmission

ABSTRACT

In a shift control system for an automatic transmission, shelf-pressure control means include means for increasing the engagement pressure of the friction elements at a first gradient as previously set after output of the shift command, wherein after output of the shift command and when start of the inertia phase is detected, a torque-reduction command is output to the torque-reduction control means, the engagement pressure at detection of the inertia phase is set as an initial shelf pressure to increase the shelf pressure at a second gradient set for each speed, and a torque variation part oil pressure is added only when detecting a variation in throttle opening, and wherein after start of the inertia phase and when completion of the inertia phase is detected, a torque-reduction completion command is output to the torque-reduction control means.  
     With this, the shelf pressure can be set appropriately during inertia phase without needing an enormous data amount even if a variation in throttle opening is present.

TECHNICAL FIELD

[0001] The present invention relates to a shift control system for anautomatic transmission having a circuit structure which can freelycontrol, during upshift, the engagement pressure to friction elementsinvolved in shifting of the automatic transmission.

BACKGROUND ART

[0002] Conventionally, there is known a shift control system for anautomatic transmission as described, for example, in a gazette JP-A2-14933. This gazette describes a technique for determining theengagement pressure of engagement-side friction elements based on thethrottle opening. With this, the engagement pressure is determined withrespect to driver's acceleration/deceleration requirement, achievingsmooth shifting. Moreover, in the prior art as disclosed in a gazetteJP-A 5-99004, it is described a technique for determining the engagementpressure with the throttle opening fixed during inertia phase.

[0003] Now, an explanation is made about requirements to be achievedwhen carrying out torque-reduction control during upshift with theengine being in the normally driving state, i.e. in the drive state socalled.

[0004] (Requirement 1) First, shift-control start determination is madeso that the engagement-side oil pressure starts to increase. When theengagement-side friction elements start to transmit torque, torque phaseis started to decrease output-shaft torque. Then, when transmissiontorque to the engagement-side friction elements which increasescontinuously exceeds to torque corresponding to input torque, theinertial phase so called is started where input rotation is increased.In the inertia phase, engine rotation and the like are lowered, so thatinertia constituents are released into output-shaft torque, resulting inan increase in output-shaft torque. As for the shape of output-shafttorque at this time, in terms of physical feel, the difference ispreferably minimized between output-shaft torque when torque is reducedmaximally in torque phase and output-shaft torque after starting theinertia phase.

[0005] (Requirement 2) Likewise, as for output-shaft torque atcompletion of the inertia phase, in terms of physical feel, thedifference is preferably minimized between output-shaft torqueimmediately before completing the inertia phase, which is determined bythe height of the engagement-side shelf pressure, and output-shafttorque immediately after completing the inertia phase, which isdetermined by input torque and the gear ratio at completion of theinertia phase.

[0006] (Requirement 3) Output-shaft torque during inertia phase ispreferably varied in accordance with the throttle opening correspondingto a driver's intention. This means that if the throttle opening isconstant, driver's acceleration/deceleration requirement is notprovided, so that output-shaft torque is preferably as nearly constantas possible within the range of failing to interfere with other tasks,whereas in the throttle opening is varied, driver'sacceleration/deceleration requirement is provided, output-shaft torqueis preferably varied in accordance with variations in engine torquewhich varies in correspondence with that requirement.

[0007] Using the technique described in the gazette JP-A 2-14933, forexample, to meet the above requirements, the requirement 3 can besatisfied. However, if the engine speed is different, input torque aftercompleting the inertia phase is different even with the same throttleopening. This renders impossible control of the relationship withoutput-shaft torque immediately before completing the inertia phase,which is determined by the shelf pressure determined in accordance withthe throttle opening, so that the requirements 1 and 2 cannot besatisfied.

[0008] Further, when supposing determination of the engagement pressurebased on input torque, the requirements 1 and 2 can be satisfied.However, turbine rotation is decreased during inertia phase, inaccordance with which input torque is increased. Thus, even when thethrottle opening is constant, and the driver has no intention to carryout acceleration or deceleration, the engagement-side oil pressure isincreased, which results in an increase in output-shaft torque, leadingto impossible achievement of an object that “if the throttle isconstant, output-shaft torque is preferably as nearly constant aspossible within the range of failing to interfere with other tasks”.

[0009] Furthermore, using the technique described in the gazette JP-A5-99004,the throttle opening is kept constant, so that the requirement 3cannot be satisfied in like manner.

DISCLOSURE OF THE INVENTION

[0010] The present invention is made in view of the above problems andrequirements, and aims to provide a shift control system for anautomatic transmission for carrying out torque-reduction control duringupshift, wherein the shelf pressure can be set appropriately duringinertia phase without needing an enormous data amount even if avariation in throttle opening is present.

[0011] In order to achieve the above object, the invention in claim 1 isdirected to a shift control system for an automatic transmissionprovided with shift control means for carrying out shifting by engagingat least one or more friction elements as released when the relationshipbetween a throttle opening of a vehicle and a vehicle speed intersects ashift line of a shift schedule, and torque-reduction control means fortemporarily educing engine torque during a period of shift transition,characterized in that it comprises shift-command determination means fordetermining whether or not a shift command is output, inertia-phasedetection means for detecting start and completion of an inertia phase,and shelf-pressure control means for controlling an engagement pressureof said friction elements, wherein said shelf-pressure control meansinclude means for increasing the engagement pressure of said frictionelements at a first gradient as previously set after output of the shiftcommand, wherein after output of the shift command and when start of theinertia phase is detected by said inertia-phase detection means, atorque-reduction command is output to said torque-reduction controlmeans, and the engagement pressure at detection of the inertia phase isset as an initial shelf pressure to increase the shelf pressure at asecond gradient as previously set, and wherein after start of theinertia phase and when completion of the inertia phase is detected bysaid inertia-phase detection means, a torque-reduction completioncommand is output to said torque-reduction control means, and theengagement pressure of said friction elements is increased up to apredetermined pressure as previously set.

[0012] With shift control system for an automatic transmission asdescribed in claim 1, the shelf-pressure control means increase theengagement pressure of the friction elements at the first gradient aspreviously set after output of the shift command. After output of theshift command and when start of the inertia phase is detected by theinertia-phase detection means, a torque-reduction command is output tothe torque-reduction control means, and the engagement pressure atdetection of the inertia phase is set as an initial shelf pressure, thusallowing setting of the shelf pressure which can reduce the differencebetween output-shaft torque at a point that torque is maximally reducedin the torque phase and output-shaft torque after starting the inertiaphase while securing progression of the inertia phase through a torquereduction, achieving a restraint of a thrusting shock and the like.

[0013] Further, like the invention as described in claim 2, the shiftcontrol system for an automatic transmission as specified in claim 1 maybe constructed so that said second gradient is determined out of atleast transmission input torque and revolution constituent at start ofthe inertia phase.

[0014] With the shift control system for an automatic transmission asspecified in claim 2, the shelf pressure is increased at the secondgradient as previously set. After start of the inertia phase and whencompletion of the inertia phase is detected by the inertia-phasedetection means, a torque-reduction completion command is output to thetorque-reduction control means, and the shelf pressure of the frictionelements is controlled at an ideal value. Moreover, the height of theoil pressure at completion of the inertia phase can be controlled by themagnitude of the second gradient set by at least input torque at startof the inertia phase, type of shifting, and revolution constituent.Therefore, the difference can be reduced between output-shaft torquedetermined by the height of the engagement-side shelf pressureimmediately before competing the inertia phase and output-shaft torqueimmediately after completing the inertia phase, achieving a restraint ofoccurrence of a shock due to an abrupt reduction in output-shaft torque.

[0015] The invention as described in claim 3 is directed to the shiftcontrol system for an automatic transmission as specified in claim 1 or2, characterized in that it comprises throttle-opening detection meansfor detecting the throttle opening, and throttle-opening variationdetermination means for determining that the throttle opening varieswhen the detected throttle opening is increased or decreased by apredetermined value or more with respect to the throttle opening at apredetermined timing after shift start determination, wherein saidshelf-pressure control means are provided with an input-torque variationcorrection part for adding/subtracting a predetermined oil pressureto/from the shelf pressure when the throttle opening is varied by thethrottle-opening variation determination means.

[0016] With the shift control system for an automatic transmission asspecified in claim 3, in the input-torque variation correction partarranged in the shelf-pressure control means, when the throttle-openingvariation determination means determine that a variation in throttleopening is present, a variation part of input torque is added to theshelf pressure to restrain a variation in output-shaft torque duringinertia phase if the throttle opening is constant. When a variation ininput torque occurs by a driver's acceleration/deceleration requirementeven during inertia phase, the variation can be reflected onoutput-shaft torque, and thus a driver's acceleration/decelerationrequirement can be reflected on output-shaft torque.

[0017] The invention as described in claim 4 is directed to the shiftcontrol system for an automatic transmission as specified in claim 3,characterized in that the predetermined oil pressure added/subtracted bysaid input-torque variation correction part is an oil pressure set inaccordance with a variation part of input torque at a present point withrespect to input torque of the automatic transmission at a point thatthe initial shelf pressure of the engagement pressure is determined.

[0018] With the shift control system for an automatic transmission asspecified in claim 4, since an increasing part with respect to inputtorque at start of the inertia phase is further added or subtracted as atorque variation part oil pressure, the difference can surely be reducedbetween output-shaft torque immediately before completing the inertiaphase and output-shaft torque immediately after completing the inertiaphase while reflecting a driver's acceleration/deceleration requirementon output-shaft torque.

[0019] The invention as described in claim 5 is directed to the shiftcontrol system for an automatic transmission as specified in claim 3 or4, characterized in that the predetermined amount of a throttlevariation is set so that the increasing side has a smaller value thanthe decreasing side.

[0020] With the shift control system for an automatic transmission asspecified in claim 5, unless the throttle opening varies by apredetermined amount as set previously on the increasing side or on thedecreasing side with respect to the throttle opening at start of theinertia phase, it is determined that driver's unintentional depressionor foot release occurs, and that the throttle opening does not vary,allowing prevention of occurrence of a shock due to driver'sunintentional depression or foot release. And the predetermined value isset so that the increasing-side value is smaller than thedecreasing-side value, allowing sure prevention of zooming of enginerotation or impossible attainment of the gear ratio due to delay ofincreasing the oil pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a general system diagram of a vehicle to which a shiftcontrol system in a first embodiment is applied;

[0022]FIG. 2 is a skeleton diagram showing a gear train of an automatictransmission with 6 forward speeds and 1 reverse speed to which theshift control system for an automatic transmission in the firstembodiment is applied;

[0023]FIG. 3 is a drawing showing an operation table of frictionelements under shift control of the shift control system for anautomatic transmission in the first embodiment is applied;

[0024]FIG. 4 is a diagram showing a hydraulic circuit and an electronicshift control system in the shift control system for an automatictransmission in the first embodiment;

[0025]FIG. 5 is a flowchart illustrating engagement-pressure controlduring upshift in the first embodiment;

[0026]FIG. 6 is a time chart illustrating engagement-pressure control atconstant throttle opening during upshift in the first embodiment;

[0027]FIG. 7 is a time chart illustrating engagement-pressure control atvaried throttle opening (on the depression side) during upshift in thefirst embodiment; and

[0028]FIG. 8 is a time chart illustrating engagement-pressure control atvaried throttle opening (on the foot release side) during upshift in thefirst embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] Based on the drawings, an explanation is made hereafter about thebest mode for achieving the shift control system for an automatictransmission according to the present invention.

FIRST EMBODIMENT

[0030]FIG. 1 is a system diagram showing a torque-reduction controlsystem, wherein 51 denotes an engine as a prime mover, and 52 denotes anautomatic transmission. Output torque of the engine 51 is input to theautomatic transmission 52 which transfers its output torque to an outputshaft 53 at the gear ratio in response to the selected speed, achievingrunning of the vehicle.

[0031] The engine 51 includes a plurality of injectors 54 for injectingfuel. Fuel injection of each injector 54 is carried out through anengine control unit 55.

[0032] The engine control unit 55 inputs essentially a signal out of anengine-speed sensor 56 for sensing an engine speed Ne, a signal out of acoolant-temperature sensor 57 for sensing an engine-coolant temperature,and a signal out of a throttle-opening sensor 58 for sensing a throttleopening TVO corresponding to an engine load to compute a fuel injectionamount, then actuates the injectors 54 separately in accordance withengine rotation by a time corresponding to the amount. It is constructedto stop actuation of ones of the injectors 54 for injecting fuel intosome cylinders as required to allow a reduction in engine output torque.

[0033] Specifically, the injectors 54 and the engine control unit 55correspond to torque changing means described in claims. In connectionwith the torque changing means, torque-reduction control may be carriedout through retard for changing ignition timing or electronic throttlecontrol for changing the throttle opening by using the electronicthrottle opening.

[0034] The automatic transmission 52 includes a control valve 59 forcontrolling shift by supplying the oil pressure or stopping its supplyto an actuator for engaging or releasing friction elements as will bedescribed later. Actuation of the control valve 59 is carried outthrough a shift control unit 64. The shift control unit 64 outputs asignal for reducing torque to the engine control unit 55 duringshifting, ensuring an improvement in shift quality and in reliability ofdurability of the friction elements pertinent to shifting.

[0035]FIG. 2 is a skeleton diagram showing a gear train of the automatictransmission 52 with 6 forward speeds and 1 reverse speed in a firstembodiment. The automatic transmission 52 uses as a gear train acombination of a simple planetary-gear set G1 and a Ravigneaux-typecompound planetary-gear set G2. The simple planetary-gear set G1comprises a first sun gear S1, a first carrier C1, and a first ring gearR1. The Ravigneaux-type compound planetary-gear set G2 comprises asecond sun gear S2, a second carrier C2, a second ring gear R2, a thirdsun gear S3, a third carrier C3, and a third ring gear R3.

[0036] An input shaft IN, to which engine tractive force is input viathe engine 51 and a torque converter, is coupled to the first ring gearR1 directly through a first member M1, and also to the third carrier C3through a second member M2 and a high clutch H/C.

[0037] The first carrier C1 is coupled to the third sun gear S3 througha third member M3, a low clutch LOW/C, and a fifth member M5, and alsoto the second sun gear S2 through the third member M3, a 3-5 reverseclutch 3-5R/C, and a sixth member M6. The sixth member M6 is fixed to atransmission casing TC through a 2-6 brake 2-6/B.

[0038] The first sun gear S1 is fixed to the transmission casing TCthrough a fourth member M4. The second carried C2 is fixed to thetransmission casing TC through a seventh member M7, a low & reversebrake L&R/B disposed in parallel, and a low one-way clutch LOW/OWC. Thethird ring gear R3 is coupled to an output gear OUT through an eighthmember M8.

[0039] The automatic transmission 52 ensures automatic shift control of6 forward speeds based on an operation point determined out of thevehicle velocity and the throttle opening and a shift schedule in theD-range position, and shift control of 1 reverse speed through selectoperation from the D-range position to the R-range position. FIG. 3shows an operation table of the friction elements in this shift control.In FIG. 3, a circular mark denotes engagement, no mark denotes release,a circular mark with X denotes engagement which occurs during enginebrake, a hatched circular mark denotes mechanical actuation duringengine driving.

[0040] First speed (1ST) is achieved by engagement of the low clutchLOW/C and the low & reverse brake L&R/B. In this case, rotation reducedthrough the input shaft IN and the first member M1 and via the simpleplanetary-gear set G1 is input to the third sun gear S3 through thethird member M3, the low clutch LOW/C, and the fifth member M5. Thethird ring gear R3 produces reduced rotation while undergoing a reactiveforce from the second carrier C2 fixed to the transmission casing TC byengagement of the low one-way clutch LOW/OWC, so that the output gearOUT outputs reduced rotation at the maximum reduction ratio through theeighth member M8.

[0041] During engine brake, the low & reverse brake L&R/B undergoes areactive force in place of the low one-way clutch LOW/OWC.

[0042] Second speed (2ND) is achieved by engagement of the low clutchLOW/C and the 2-6 brake 2-6/B. In this case, rotation reduced throughthe input shaft IN and the first member M1 and via the simpleplanetary-gear set G1 is input to the third sun gear S3 through thethird member M3, the low clutch LOW/C, and the fifth member M5. Thethird ring gear R3 produces reduced rotation while undergoing a reactiveforce from the second sun gear S2 fixed to the transmission casing TC byengagement of the 2-6 brake 2-6/B, so that the output gear OUT outputsreduced rotation at a smaller reduction ratio than that of the firstspeed through the eighth member M8.

[0043] Third speed (3RD) is achieved by engagement of the low clutchLOW/C and the 3-5 reverse clutch 3-5R/C. In this case, rotation reducedthrough the input shaft IN and the first member M1 and via the simpleplanetary-gear set G1 is input to the third sun gear S3 through thethird member M3, the low clutch LOW/C, and the fifth member M5, and tothe second sun gear S2 through the third member M3, the 3-5 reverseclutch 3-5R/C, and the sixth member M6. Since the Ravigneaux-typecompound planetary-gear set G2 becomes in the directly coupled state,the third ring gear R3 is rotated in the same rotation as the two sungears S2, S3, so that the output gear OUT outputs reduced rotation at asmaller reduction ratio than that of the second speed through the eighthmember M8.

[0044] Fourth speed (4TH) is achieved by engagement of the low clutchLOW/C and the high clutch H/C. In this case, on the one hand, rotationreduced through the input shaft IN and the first member M1 and via thesimple planetary-gear set G1 is input to the second sun gear S2 throughthe third member M3, the 3-5 reverse clutch 3-5R/C, and the sixth memberM6. On the other hand, the same rotation as that of the input shaft INis input to the third carrier C3 through the input shaft IN, the secondmember M2, and the high clutch H/C. The third ring gear R3 is rotated byrotation between the two input rotations, so that the output gear OUToutputs slightly reduced rotation with respect to input rotation throughthe eighth member M8.

[0045] Fifth speed (5TH) is achieved by engagement of the 3-5 reverseclutch 3-5R/C and the high clutch H/C. In this case, on the one hand,rotation reduced through the input shaft IN and the first member M1 andvia the simple planetary-gear set G1 is input to the second sun gear S2through the third member M3, the 3-5 reverse clutch 3-5R/C, and thesixth member M6. On the other hand, the same rotation as that of theinput shaft IN is input to the third carrier C3 through the input shaftIN, the second member M2, and the high clutch H/C. The third ring gearR3 is restrained and rotated by the two input rotations, so that theoutput gear OUT outputs slightly increased rotation with respect toinput rotation through the eighth member M8.

[0046] Sixth speed (6TH) is achieved by engagement of the high clutchH/C and the 2-6 brake 2-6/B. In this case, the same rotation as that ofthe input shaft IN is input to the third carrier C3 only through theinput shaft IN, the second member M2, and the high clutch H/C. The thirdring gear R3 produces increased rotation while undergoing a reactiveforce from the second sun gear S2 fixed to the transmission casing TC byengagement of the 2-6 brake 2-6/B, so that the output gear OUT outputsfurther increased rotation with respect to rotation at the fifth speedthrough the eighth member M8.

[0047] Reverse speed (REV) is achieved by engagement of the 3-5 reversecutch 3-5/R/C and the low & reverse brake L&R/B. In this case, rotationreduced through the input shaft IN and the first member M1 and via thesimple planetary-gear set G1 is input to the second sun gear S2 throughthe third member M3, the 3-5 reverse clutch 3-5R/C, and the sixth memberM6. The third ring gear R3 produces reverse rotation while undergoing areactive force from the second carrier C2 fixed to the transmissioncasing TC by engagement of the low & reverse brake L&R/B, so that theoutput gear OUT outputs reduced reverse rotation through the eighthmember M8.

[0048] Next, with reference to FIG. 4, the structure is explained abouta hydraulic circuit and an electronic shift control system which achievethe above shift control. In FIG. 4, 1 is an engagement piston chamber ofthe low clutch LOW/C, 2 is an engagement piston chamber of the highclutch H/C, 3 is an engagement piston chamber of the 2-6 brake 2-6/B, 4is an engagement piston chamber of the 3-5 reverse clutch 3-5R/C, and 5is an engagement piston chamber of the low & reverse brake L&R/B. Thelow clutch LOW/C, the high clutch H/C, the 2-6 brake 2-6/B, the 3-5reverse brake 3-5R/C, and the low & reverse brake L&R/B are engaged bysupplying to the engagement piston chambers 1-5 the engagement pressurewhich is in the form of D-range pressure or R-range pressure,respectively. And they are released by removing the engagement pressure.

[0049] The D-range pressure is a line pressure through a manual valve16, and occurs only when selecting the D range. The R-range pressure isa line pressure through the manual valve 16, and occurs only whenselecting the R range. At a range other than the R range, no oilpressure occurs due to connection to a drain port.

[0050] In FIG. 4, 6 is a first hydraulic control valve for controllingthe engagement pressure to the low clutch LOW/C, 7 is a second hydrauliccontrol valve for controlling the engagement pressure to the high clutchH/C, 8 is a third hydraulic control valve for controlling the engagementpressure to the 2-6 brake 2-6/B, 9 is a fourth hydraulic control valvefor controlling the engagement pressure to the 3-5reverse clutch 3-5R/C,and 10 is a fifth hydraulic control valve for controlling the engagementpressure to the low & reverse brake L&B.

[0051] The first hydraulic control valve 6 comprises a first dutysolenoid 6 a for creating the shift control pressure using the pilotpressure as source pressure and by dint of a solenoid force, and a firstpressure regulating valve 6 b for regulating the low-clutch pressureusing the D-range pressure as source pressure and the shift controlpressure and feedback pressure as operation signal pressure. The firstduty solenoid 6 a puts the low-clutch pressure zero when the solenoid isturned off, and increases the low-clutch pressure with increase in ONduty ratio when the solenoid is turned on.

[0052] The second hydraulic control valve 7 comprises a second dutysolenoid 7 a for creating the shift control pressure using the pilotpressure as source pressure and by dint of a solenoid force, and asecond pressure regulating valve 7 b for regulating the high-clutchpressure using the D-range pressure as source pressure and the shiftcontrol pressure and feedback pressure as operation signal pressure. Thesecond duty solenoid 7 a puts the high-clutch pressure zero when thesolenoid is turned on (100% ON duty ratio), increases the high-clutchpressure with decrease in ON duty ratio, and puts the high-clutchpressure at a maximum pressure when the solenoid is turned off.

[0053] The third hydraulic control valve 8 comprises a third dutysolenoid 8 a for creating the shift control pressure using the pilotpressure as source pressure and by dint of a solenoid force, and a thirdpressure regulating valve 8 b for regulating the 2-6 brake pressureusing the D-range pressure as source pressure and the shift controlpressure and feedback pressure as operation signal pressure. The thirdduty solenoid 8 a puts the 2-6 brake pressure zero when the solenoid isturned off, and increases the 2-6 brake pressure with increase in ONduty ratio.

[0054] The fourth hydraulic control valve 9 comprises a fourth dutysolenoid 9 a for creating the shift control pressure using the pilotpressure as source pressure and by dint of a solenoid force, and afourth pressure regulating valve 9 b for regulating the 3-5reverse-clutch pressure using the line pressure as source pressure andthe shift control pressure and R-range pressure as operation signalpressure. The fourth duty solenoid 9 a puts the 3-5 reverse-clutchpressure zero when the solenoid is turned on (100% ON duty ratio),increases the 3-5 reverse-clutch pressure with decrease in ON dutyratio, and puts the 3-5 reverse-clutch pressure at a maximum pressurewhen the solenoid is turned off.

[0055] The fifth hydraulic control valve 10 comprises a fifth dutysolenoid 10 a for creating the shift control pressure using the pilotpressure as source pressure and by dint of a solenoid force, and a fifthpressure regulating valve 10 b for regulating the low & reverse brakepressure using the D-range pressure or the R-range pressure as sourcepressure and the shift control pressure and feedback pressure asoperation signal pressure. The fifth duty solenoid 10 a puts the low &reverse brake pressure zero when the solenoid is turned off, andincreases the low & reverse brake pressure with increase in ON dutyratio.

[0056] In FIG. 4, 11 is a first pressure switch (oil-pressure detectingmeans), 12 is a second pressure switch (oil-pressure detecting means),13 is a third pressure switch (oil-pressure detecting means), 14 is afourth pressure switch (oil-pressure detecting means), 15 is a fifthpressure switch (oil-pressure detecting means), 16 is manual valve, 17is a pilot valve, 19 is a line-pressure passage, 20 is a pilot-pressurepassage, 21 is a D-range pressure passage, 22 is an R-range pressurepassage, 23 is a D & R range pressure passage, 24 is a low-clutchpressure passage, 25 is a high-clutch pressure passage, 26 is a 2-6brake-pressure passage, 27 is a 3-5 reverse-clutch pressure passage, and28 is a low & reverse brake-pressure passage.

[0057] Specifically, the low-clutch pressure passage 24, the high-clutchpressure passage 25, the 2-6 brake-pressure passage 26, the 3-5reverse-clutch pressure passage 27, and the low & reverse brake-pressurepassage 28 are provided with the first to fifth pressure switches 11-15for detecting the presence or absence of the engagement pressure througha switch signal (ON when the engagement-pressure is present, and OFFwhen the engagement pressure is absent), respectively.

[0058] In FIG. 4, 40 is an A/T control unit (shift control means), and50 is a shift lever. The shift lever 50 has ranges such as P range wherea transmission output shaft is locked at stop of the vehicle, R rangewhere the reverse speed is achieved, N range where the neutral state isachieved which shows a state that forward or backward movement ispossible without outputting torque input from the engine, D range wherethe forward speeds are achieved, and engine-brake range where the low &reverse brake L&R/B is controlled for engagement at the first speed. Theshift lever 50 is coupled to the manual valve 16, wherein driver'soperation of shift lever 50 causes switching of the position of themanual valve 16, achieving a target shift state.

[0059] In the drawing, 41 is a vehicle-velocity sensor (transmissionoutput-shaft revolution sensor), 42 is a throttle sensor for sensing thethrottle opening, 43 is an engine-speed sensor for sensing the enginespeed, 44 is a turbine-revolution sensor (transmission input-shaftrevolution sensor) for sensing the turbine revolution, 45 is aninhibitor switch for detecting the range position of the shift lever 50,and 46 is an oil-temperature sensor for sensing the oil temperature inthe transmission, which constitute the electronic shift control system.The A/T control unit 40 inputs switch signals out of the pressureswitches 11, 12, 13, 14, 15 and signals out of the sensors/switch 41,42, 43, 44, 45, 46 to carry out processing based on such inputinformation, preset shift control formula and fail-safe control formulaand the like. In accordance with the processing results, solenoid drivesignals are output to the first duty solenoid 6 a, the second dutysolenoid 7 a, the third duty solenoid 8 a, the fourth duty solenoid 9 a,and the fifth duty solenoid 10 a.

[0060] Next, operation is explained.

[0061]FIG. 5 is a flowchart showing flow of shelf-pressure controlprocessing when torque-reduction control during upshift is carried out,which is executed in the A/T control unit 40. The steps are explainedbelow.

[0062] At a step 101, it is determined whether or not control ofgradient for torque phase for upshift is carried out. If it is undercontrol of gradient for torque phase for upshift, flow proceeds to astep 102. Otherwise, flow proceeds to a step 107.

[0063] At the step 102, the command oil pressure is increased at agradient for torque phase. This gradient for torque phase is a gradientset previously in accordance with the type of shifting and transmissioninput torque.

[0064] At a step 103, it is determined whether or not the inertia phaseis started. If the inertia phase is started, flow proceeds to a step104, whereas if it is not started, the control is finished.

[0065] At the step 104, the oil pressure when the inertia phase isdetected is set as an initial shelf pressure, wherein a command pressureserves as the initial shelf pressure.

[0066] At a step 105, it is carried out determination on completion ofcontrol of gradient for torque phase.

[0067] At a step 106, a torque reduction is started.

[0068] At the step 107, it is determined whether or not the inertiaphase is completed. If the inertial phase is completed, flow proceeds toa step 113, whereas if it is not completed, flow proceeds to a step 108.

[0069] At a step 109, throttle variation determination is carried out.If it is determined that there is a variation in throttle opening, flowproceeds to a step 110, whereas if it is determined that there is novariation in throttle opening, flow proceeds to a step 111.

[0070] In order to prevent occurrence of a shock due to driver'sunintentional depression or foot release, unless the throttle openingvaries by a predetermined amount as set previously on the increasingside or on the decreasing side with respect to the throttle opening atstart of the inertia phase after shift start determination as shown inthe time chart, it is determined that driver's unintentional depressionor foot release occurs, and that the throttle opening does not vary. Thepredetermined value is set so that the increasing-side value is smallerthan the decreasing-side value. This is because a delayed increase inoil pressure on the increasing side produces zooming of engine rotationor impossible attainment of the gear ratio, i.e. for preventing this.

[0071] At the step 110, the command oil pressure is set at an oilpressure obtained by adding a torque variation part oil pressure and ashelf-pressure gradient part oil pressure to the shelf pressure.

[0072] Here, the shelf-pressure gradient part oil pressure is previouslyset in a map for each type of shifting, e.g. turbine revolution at startof the inertia phase and transmission input torque, and it is determinedwith reference thereto. The shelf-pressure gradient part oil pressure aspreviously set is preferably set to have a gradient which allows thedifference from torque after completing the inertial phase to beminimized. By way of example, since output-shaft torque after completingthe inertia phase can previously calculated from the gear ratio of anext speed, transmission input torque, and a revolution constituent(vehicle velocity or turbine revolution) at start of the inertia phase,an increase gradient of the engagement pressure is set to roughlycoincide with a gradient connecting to output-shaft torque aftercompleting the inertia phase, i.e. output-shaft torque of a next speed.

[0073] The torque variation part oil pressure is an oil pressurecorresponding to an increase/decrease part of transmission input torqueat throttle variation determination with respect to that at start of theinertia phase, and is calculated, for example, by multiplyingtransmission input torque by torque-converter torque ratio, which isfurther multiplied by a predetermined coefficient.

[0074] At the step 111, the command oil pressure is set at an oilpressure obtained by adding the shelf-pressure gradient part oilpressure to the initial shelf pressure.

[0075] At a step 112, the command oil pressure is output to thesolenoids.

[0076] At a step 114, a torque reduction is completed.

[0077]FIGS. 6, 7, and 8 are time charts illustrating the throttleopening, gear ratio, engagement-side command pressure, torque-reductionamount, and output-shaft torque when the above shelf-pressure control iscarried out. The time charts are explained below.

[0078]FIG. 6 is time chart illustrating shelf-pressure control when nothrottle variation is present. Specifically, at the step 101 to the step106, when a shift command is output to start control of gradient fortorque phase, the command oil pressure is increased at a gradient fortorque phase. With the inertia phase started, the command oil pressureat that point is set as an initial shelf pressure. At this time, atorque reduction is started, the amount of which has a map as previouslyset in accordance with the type of shifting, and is determined withreference thereto.

[0079] At the step 103, it is determined that the inertia phase isstarted, and at the step 109, it is determined whether or not there is avariation in throttle opening. In FIG. 6, since it is a case where nothrottle variation is present, flow proceeds to the step 111 where theoil pressure obtained by adding the shelf-pressure gradient part oilpressure to the initial pressure is output as a command oil pressure.And at the step 107, if it is determined that the inertia phase iscompleted, a torque reduction is completed, and the control is finished.

[0080]FIG. 7 is time chart illustrating shelf-pressure control when athrottle variation is present. Specifically, at the step 101 to the step106, when a shift command is output to start control of gradient fortorque phase, the command oil pressure is increased at a gradient fortorque phase. With the inertia phase started, the command oil pressureat that point is set as an initial shelf pressure for outputting, and atorque reduction is started.

[0081] At the step 103, it is determined that the inertia phase isstarted, and at the step 109, it is determined whether or not there is avariation in throttle opening. In FIG. 7, since a variation occurs onthe throttle-opening increasing side over a predetermined value aspreviously set, it is determined that the throttle opening varies, andflow proceeds to the step 110 where the oil pressure obtained by addingthe shelf-pressure gradient part oil pressure and the torque variationpart oil pressure to the initial shelf pressure is output as a commandoil pressure. Here, addition of the torque variation part oil pressureallows achievement of shifting in such a manner that the difference fromoutput-shaft torque after completing the inertia phase at completion ofthe inertia phase is decreased by increasing the engagement-side commandpressure even if the throttle opening is depressed to increase inputtorque to the transmission and thus input torque to the engagementelements. And at the step 107, if it is determined that the inertiaphase is completed, a torque reduction is completed, and the control isfinished.

[0082]FIG. 8 is a time chart illustrating shelf-pressure control when athrottle variation is present. Specifically, at the step 101 to the step106, when a shift command is output to start gradient for torque phase,the command oil pressure is increased at a gradient for torque phase.With the inertia phase started, the command oil pressure at that pointis set as an initial shelf pressure for outputting, and a torquereduction is started.

[0083] At the step 103, it is determined that the inertia phase isstarted, and at the step 109, it is determined whether or not there is avariation in throttle opening. In FIG. 8, since a variation occurs onthe throttle-opening decreasing side over a predetermined value aspreviously set, it is determined that the throttle opening varies, andflow proceeds to the step 110 where the oil pressure obtained by addingthe shelf-pressure gradient part oil pressure and the torque variationpart oil pressure to the initial shelf pressure is output as a commandoil pressure. In this case, since torque is reduced, the torquevariation part oil pressure is a negative value. When this issubtracted, the command oil pressure is decreased in a concretivemanner. Here, addition of the torque variation part oil pressure allowsachievement of shifting in such a manner that the difference fromoutput-shaft torque after completing the inertia phase at completion ofthe inertia phase is decreased by decreasing the engagement-side commandpressure even if the throttle opening is released to decrease inputtorque to the transmission and thus input torque to the engagementelements. And at the step 107, if it is determined that the inertiaphase is completed, a torque reduction is completed, and the control isfinished.

[0084] As explained above, with the shift control system for anautomatic transmission described in the first embodiment, the engagementpressure at detection of the inertia phase is set as an initial shelfpressure, so that the shelf pressure can be set which allows minimumdifference between output-shaft torque at a point that torque ismaximally reduced in the torque phase and output-shaft torque afterstarting the inertia phase while securing progression of the inertiaphase through a torque reduction, achieving a restraint of a thrustingshock and the like at start of the inertia phase (effect correspondingto claim 1).

[0085] Further, the initial shelf pressure of the friction elements iscontrolled at an ideal value as described above, and the height of theoil pressure at completion of the inertia phase can be controlled by ashelf-pressure gradient set by input torque at start of the inertiaphase, type of shifting, and revolution constituent. Therefore, thedifference can be reduced between output-shaft torque determined by theheight of the engagement-side shelf pressure immediately beforecompleting the inertia phase and output-shaft torque determined by thegear ratio, input torque, and revolution constituent after shiftingimmediately after completing the inertia phase, achieving a restraint ofoccurrence of a shock due to an abrupt reduction in output-shaft torque(effect corresponding to claim 2).

[0086] Still further, when it is determined a throttle variation on thethrottle-opening increasing side, the torque variation part oil pressureis further added in addition to the initial shelf pressure and theshelf-pressure gradient part oil pressure. When the throttle opening isconstant, it is determined that the driver expects constant output-shafttorque, a variation in output-shaft torque is restrained during inertiaphase, so that when a driver's acceleration/deceleration requirementoccurs even during inertia phase, it is possible to achieve an increasein output-shaft torque in response to this requirement, obtainingreflection of the driver's acceleration/deceleration requirement onoutput-shaft torque (effect corresponding to claim 3).

[0087] Furthermore, since an increasing part with respect to inputtorque at start of the inertia phase is added or subtracted as torquevariation part oil pressure, the difference can surely be reducedbetween output-shaft torque immediately before completing the inertiaphase and output-shaft torque immediately after completing the inertiaphase while reflecting a driver's acceleration/deceleration requirementon output-shaft torque (effect corresponding to claim 4).

[0088] Further, unless the throttle opening varies by a predeterminedamount as set previously on the increasing side or on the decreasingside with respect to the throttle opening at start of the inertia phase,it is determined that driver's unintentional depression or foot releaseoccurs, and that the throttle opening does not vary, allowing preventionof occurrence of a shock due to driver's unintentional depression orfoot release. And the predetermined value is set so that theincreasing-side value is smaller than the decreasing-side value,allowing sure prevention of zooming of engine rotation or impossibleattainment of the gear ratio due to delay of increasing the oil pressure(effect corresponding to claim 5).

ANOTHER EMBODIMENT

[0089] Having explained the shift control system for an automatictransmission of the present invention in accordance with the firstembodiment, the concrete structure is not limited to the firstembodiment, and design modification, addition and the like are allowedwithout departing from the gist of the inventions in claims.

[0090] By way of example, the first embodiment shows an example ofapplication to the automatic transmission of 6 forward speeds and 1reverse speed. Optionally, it is applicable to an automatic transmissionhaving 6 forward speeds similarly, but different structure, or anautomatic transmission of 4 forward speeds, 5 forward speeds, 7 forwardspeeds or the like.

1. A shift control system for an automatic transmission provided withshift control means for carrying out shifting by engaging at least oneor more friction elements as released when the relationship between athrottle opening of a vehicle and a vehicle speed intersects a shiftline of a shift schedule, and torque-reduction control means fortemporarily reducing engine torque during a period of shift transition,characterized in that it comprises shift-command determination means fordetermining whether or not a shift command is output, inertia-phasedetection means for detecting start and completion of an inertia phase,and shelf-pressure control means for controlling an engagement pressureof said friction elements, wherein said shelf-pressure control meansinclude means for increasing the engagement pressure of said frictionelements at a first gradient as previously set after output of the shiftcommand, wherein after output of the shift command and when start of theinertia phase is detected by said inertia-phase detection means, atorque-reduction command is output to said torque-reduction controlmeans, and the engagement pressure at detection of the inertia phase isset as an initial shelf pressure to increase the shelf pressure at asecond gradient as previously set, and wherein after start of theinertia phase and when completion of the inertia phase is detected bysaid inertia-phase detection means, a torque-reduction completioncommand is output to said torque-reduction control means, and theengagement pressure of said friction elements is increased up to apredetermined pressure as previously set.
 2. The shift control systemfor an automatic transmission as specified in claim 1, characterized inthat said second gradient is determined out of at least transmissioninput torque and revolution constituent at start of the inertia phase.3. The shift control system for an automatic transmission as specifiedin claim 1 or 2, characterized in that it comprises throttle-openingdetection means for detecting the throttle opening, and throttle-openingvariation determination means for determining that the throttle openingvaries when the detected throttle opening is increased or decreased by apredetermined value or more with respect to the throttle opening at apredetermined timing after shift start determination, wherein saidshelf-pressure control means are provided with an input-torque variationcorrection part for adding/subtracting a predetermined oil pressureto/from the shelf pressure when the throttle opening is varied by thethrottle-opening variation determination means.
 4. The shift controlsystem for an automatic transmission as specified in claim 3,characterized in that the predetermined oil pressure added/subtracted bysaid input-torque variation correction part is an oil pressure set inaccordance with a variation part of input torque at a present point withrespect to input torque of the automatic transmission at a point thatthe initial shelf pressure of the engagement pressure is determined. 5.The shift control system for an automatic transmission as specified inclaim 3 or 4, characterized in that the predetermined amount of athrottle variation is set so that the increasing side has a smallervalue than the decreasing side.
 6. The shift control system for anautomatic transmission as specified in claim 2, characterized in that itcomprises throttle-opening detection means for detecting the throttleopening, and throttle-opening variation determination means fordetermining that the throttle opening varies when the detected throttleopening is increased or decreased by a predetermined value or more withrespect to the throttle opening at a predetermined timing after shiftstart determination, wherein said shelf-pressure control means areprovided with an input-torque variation correction part foradding/subtracting a predetermined oil pressure to/from the shelfpressure when the throttle opening is varied by the throttle-openingvariation determination means.
 7. The shift control system for anautomatic transmission as specified in claim 4, characterized in thatthe predetermined amount of a throttle variation is set so that theincreasing side has a smaller value than the decreasing side.